Stock for the roll forming of variable thickness sections is usually made by one of two processes. By passing stock through a variable nip of forming rolls, symmetrically tapered stock is created. By symmetrically tapered stock, it is meant stock which enlarges symmetrically from the center or thinner portions of the stock to form the thicker portions. Symmetrically tapered stock also decreases in thickness symmetrically toward the center of the stock from each opposite side of the stock.
Another method of making stock for variable thickness roll forming is to lay a uniform thickness piece of stock on the bed of a milling machine and then mill away the top surface of the stock in areas where it is not needed. The latter is of course quite expensive and creates a reference plane or flat surface on one side only. Symmetrically tapered stock has no flat surface or reference plane. Symmetrically tapered stock, of course, has a multiplicity of planes, but none are oriented for roll forming to the required sectional shape.
The present invention is useful with stock either symmetrically tapered or milled as indicated above to convert the stock into stock having datum or reference planes which facilitate the roll forming of the stock to maintain closely the required constant dimensions and also to minimize the lack of linearity or wavy surfaces normally found in roll formed variable thickness stock.